Student Chapter • American Association of Equine Practitioners New York State College of Veterinary Medicine • Cornell University

PUNKIES, PIN WORMS, AND OTHER PARASITES: A Look at Parasite Induced Skin Diseases

By Luba Drouin, '87

Equine skin diseases can interfere with the horse's appearance, comfort, and ability to perform to capacity. This can be very annoying to the horse, the owner and the veterinarian. Parasites such as the horse stomach worm, lice and pinworms can manifest themselves as skin disease. This article deals with several parasite-induced skin diseases (dermatoses), how they occur, and their diagnosis, treatment and prevention.

Cutaneous Habronemiasis

More commonly known as summer sores, cutaneous habronemiasis is a skin disease associated with the horse stomach worms, muscae and Habronema majus, and Draschia magastoma, that have a symbiotic relationship with the house- and stable-. The normal destination they usually die. The horse's female stomach worm produces larvae that are immune system mounts an inflammatory passed in the equine host's feces and ingested response to the larvae in the surrounding tissue by the larvae of house or stable which live leading to the formation of an itchy, yellowish in manure deposits. The worm larvae then take ulcerated lesion and granulation tissue. up residence within the fly larvae. The cycle is completed when the fly larvae hatch into adult Treatment of these lesions can require flies and deposit the stomach worm larvae surgical removal when there is excessive around a horse's mouth. The horse swallows the granulation. Early in the process, as well as in stomach worm larvae that pass to the stomach areas where surgical excision is difficult, where they mature into adults. corticosteroids (cortisone-like drugs) are used to quiet down the immune system and hence Summer sores occur when these worm reduce the inflamatory response and itch. larvae are attached to areas of damaged skin on Recently, ivermectin has been reported to be the legs, around the eyes, and the prepuce. The beneficial in the treatment of habronemiasis. flies deposit the larvae of the stomach worm in Due to the locations of these granulomatous the damaged skin and the larvae penetrate the lesions, cryosurgery has proven to be more dermis, but since they are far from their effective than conventional surgical techniques. EQUINE B o u n d s

Prevention requires strict fly control on the horse and in its environment. Wounds should receive immediate attention, be bandaged when possible and kept clean to discourage the flies from landing on the site. Paste worming with ivermectin will also decrease the adult parasite population in the stomach and decrease the number of larvae available to the fly population.

Onchocerciasis

Onchocerciasis is another parasite- induced equine dermatosis. Onchocerca cervicalis is a worm that lives in the ligamentum nuchae or thick, fibrous, supporting structure of the neck muscles in horses. The adult worms produce microfilariae that migrate through the connective tissue to the skin of the belly midline, face, and eyes. When these microfilaria die, the body's inflammatory response produces swelling and redness followed by ulceration. The horse may experience itching, oozing and crusting of lesions, resulting treatment. Since the actual damage in the eye in loss of hair and skin pigment. If the as well as in the skin is caused by the body's microfilaria are migrating through the eye inflammatory response to the foreign antigen, when they die this can result in multiple eye the microfilariae, the severity of the outcome problems. can be decreased by treating with corticosteroids prior to treating with Most horses have some Onchocerca ivermectin. Corticosteroids will decrease the microfilariae in their connective tissue. Some inflammatory response and itching and lessen horses however seem to form an allergic skin damage. response against the outer coat of the microfilariae. These horses have an Culicoides Hypersensitivity overwhelming allergic inflammatory reaction resulting in the cutaneous damage mentioned Culicoides hypersensitivity has a seasonal above. occurence associated with the culicoides gnats (also called punkies and no-see-ums) during Onchocerchiasis can be treated summer months. The disease is caused by a systemically with ivermectin. Since the disease hypersensitivity (allergic) reaction to the saliva is believed to be due to the continuous death of of these gnats. They usually feed on the the microfilariae, killing large numbers of dorsum of the horse producing a pruritic microfilariae at once will give the horse a dermatitis that leads to excoriation, crusting, break from the disease. But horseowners should scaling and alopecia and erythema on the exercise caution in the use of ivermectin if the forehead, neck, withers, shoulders, rump, and horse is having eye problems along with the skin base of the tail. Many of these lesions are problems. Ivermectin will kill the microfilariae secondary to the self trauma inflicted by migrating through the eye and this could result rubbing, especially in the tail and mane areas. in serious eye problems. A veterinarian should Mosquito or black fly saliva may also affect examine the eyes prior to ivermectin some horses in the same way. EQUINE B o u n d s

There may be a hereditary predisposition in that some families of horses may be more sensitive to gnat, black fly and mosquito bites.

Treatment involves intensive control. These almost microscopic are found in areas of high humidity and around water. They like to feed in the evening hours, so pasturing horses in the evening will actually expose them to these pests. If this is a serious problem on the farm it would be helpful to stable horses from dusk to dawn. Diligent application of repellents may help lessen the sensitivity. Mosquito screens are not effective because gnats readily pass through them. Corticosteroids are often needed to control severe itching.

Oxyurias associated with itching. Lice are usually found on the neck around the mane, but can be Caused by Oxyuris equi or pin worms, present anywhere. oxyurias leads to an anal itching that results in constant tail rubbing. The adult worms live in Because most infections occur through the large bowel of the horse, but the female close contact, affected should be migrates out to the anus and deposits her eggs isolated to prevent spread of the parasites. in the anal area. The itching caused by the Horse lice are very host specific and will not presence of the pinworm eggs leads to tail live on other species, however, they can live rubbing producing erosions, redness and broken without a host for up to 2 weeks so it is possible hairs around the base of the tail, symptoms to spread lice infection through contaminated much like that of culicoides hypersensitivity. brushes and tack. Application of water-based, However, finding eggs of the pin worm around organophosphate insecticides is the approved the anus will help identify oxyuriasis. To find treatment, but administering a water bath the eggs of Oxyuris equi place scotch tape on during the cold winter months is not appealing the anal region and examine it under a to man or beast. Thus insecticidal powders are miscroscope. commonly used. This may be why it is difficult to rid the of lice in winter. In the Lice summer, the problem will usually resolve.

Lice infestation usually occurs during the Perhaps the most difficult aspect of skin winter months. This is probably due to the diseases, especially those that are parasite- horses' long hair coats, close animal contact, induced, is finding the cause. But with and even the stress of cold weather. persistence it is possible to get to the root of the itch, treat it, and work to prevent it in the There are two types of lice: biting lice, future. Damalina equi, and sucking lice, Haematopinus asini. Biting lice usually cause itching and hair loss and excoriation secondary to the itching. Luba Drouin, student editor of this issue of Sucking lice may cause anemia due to the Equine Rounds, is beginning her final year in blood loss during feeding and hair damage the DVM program. EQUINE TtOUNDS

LUMPS & BUMPS maximal size. Earlier removal may result in recurrence and stimulation of growth. Many By Corine Farewell '89 chemical treatments and wart vaccines have been advocated, but their value is disputed.

Sarcoids Horses are subject to a variety of conditions which result in the formation of Sarcoids are the most common neoplasm neoplasms on the skin surface. Neoplasia can in horses. They are fibrous, locally aggressive be defined as an uncontrolled multiplication of tumors which have a predilection for the skin of cells which form a mass or growth. Although the limbs, head, neck and chest, but may occur some of these are of little consequence to the on any body surface. Similar to the papilloma, well-being of the animal, others may be life- sarcoids are also induced by a virus and only threatening. Some of the more common occasionally regress spontaneously. neoplastic "lumps and bumps" on horses are: Sarcoids are classified into four types: Papilloma verrucous, fibroblastic, mixed fibroblastic and verrucous and occult. Verrucous sarcoids Commonly referred to as "warts," these resemble a wart and are recognized as a growth small growths are caused by a virus which has a on or above the skin level. The verrucous type predilection for the muzzle, lips and eyelids. In may be confused with a papilloma at the onset severe cases, the warts may extend back to the of growth. When the verrucous sarcoid is jowl and even on the chest and front legs. injured, it may grow quickly into a fibrous (fibroblastic) sarcoid or a mixed At the onset of the disease, the warts are fibroblastic/verrucous sarcoid. small, grey cauliflower-like growths with a short stem. As the warts reach the end of their Fibroblastic type sarcoids are normal 3-4 month lifespan, there is a minor distinguished as hard nodules in the skin. Early change in color to pinkish grey. Once they on, the nodules rarely exceed 1-2 inches in change color, they are usually sloughed within 3 diameter until trauma (accidental or surgical) to 4 weeks. or normal surface erosion of the skin leads to typical fibrous growth. There is considerable The horses most commonly affected are spread over the area, and the tumors may between 9 and 12 months of age. The warts do become quite large. Surface areas of over 10 not cause a real problem to the young horse, inches have been reported for fibroblastic-type but extra care in handling these horses is sarcoids. Sarcoids with both verrucous and necessary. Growths on the lips will restrict the fibroblastic characteristics are rare. They are use of a twitch. usually seen when verrucous type sarcoids are evolving into fibroblastic type sarcoids after Papillomas are spread through contact having been traumatized. Occult sarcoids are with other horses, or from paddocks and stalls the most deceptive in clinical appearance. where affected horses have been stabled. These lesions occur as a localized area of slight thickening of the skin and hair loss. They are Treatment involves keeping affected frequently misdiagnosed as dermatophytosis areas clean and free of flies to avoid secondary (ringworm). infection in the normal 3-4 month lifespan of the papilloma. If removal is desired for There are many treatments for sarcoids cosmetic reasons, it is recommended that the ranging from topical medication to elaborate operation be performed when the wart is at surgical techniques. Currently, the most 5 rf \ EQUINE m v B o u n d s

region of the eye. Squamous cell carcinoma will appear differently in different regions of the body, but in all cases ulceration, failure to heal, necrosis, and a foul odor is associated with the growth.

Squamous cell carcinomas are usually slow-growing and slow to metastasize or spread to other body organs. These characteristics make surgical remoyal a reasonable treatment. However,'“ tumors often recur. Squamous cell carcinomas have also been successfully treated with radiotherapy (which uses radioactive implants to kill cancer cells), cryosurgery, and hyperthermia or the use of radio frequency current to induce a rise in temperature that kills the cancer cells.

Fibroma and Fibrosarcoma

Fibromas are benign tumors made up of fibrous connective tissue while fibrosarcomas Melanomas are most commonly seen in gray are the malignant form of the fibroma. These and white horses, but may occur in colored growths can be found on horses of any age. horses as well. Generally they are located on the lower limbs, lateral limbs and chest, prepuce, penis and occasionally on the sole surface or in the frog of the foot. They appear as hard growths under successful methods for treating sarcoids are the skin or as wart-like or cauliflower-like cryosurgery, which uses extremely cold growths on the skin. In the frog or foot they temperatures to freeze and kill the diseased appear as granular growths. Surgical removal is tissue, and intralesional injections of killed recommended. bacterial products, which are thought to stimulate local immunity and inflammation. Mastocytoma

Squamous Cell Carcinoma Mastocytomas are tumors composed of dermal mast cells. The cause of these tumors These tumors occur mostly in horses over is unknown. They occur in horses of any breed three years old with unpigmented or poorly or age, and most commonly in males. Lesions pigmented skin and excessive exposure to are usually solitary, and have a predilection for ultraviolet light (sunshine) is believed to be an the head, neck, and legs. These tumors may be important causative factor. At the onset this hard swellings with the overlying skin being tumor is a small, granulating, non-healing sore normal, or they may be hairless and ulcerated. in the skin. Eventually the tumor enlarges and may protrude above the level of the skin, Equine mastocytomas appear to be benign particularly when in the area of the eye, penis and metastasis has never been reported. or vulva. The appearance of small white Treatment may include (1) surgical excision, (2) slightly raised plaques has been noted as a pre- radiotherapy, and (3) sulesional injections of cancerous change on the penis, vulva and in the corticosteroids. EQUINE B o u n d s

Summertime Blues By Annemarie Bimbo '87

Summertime is a very common time of Melanoma year to notice lumps and bumps on your horse's body. There are numerous causes of these Melanomas are most commonly seen in bumps, and they are not easily distinguished by ray and white horses, but may occur in colored their appearance alone. It is most helpful to orses as well. These tumors that may be benign or malignant, originate from melanin- or provide to your veterinarian as complete a pigment-forming cells found in the skin. The history as possible. The following are some of first signs are small, hard, black swellings the questions you may be asked: When did the bumps first appear? What was their appearance around the anus, vulva, hairless region of the when they first erupted? How fast have they tail, the parotid gland area, and occasionally an progressed? Is the horse itchy? Have there isolated tumor anywhere on the body. Benign been any changes in the horse's feed or tumors do not infiltrate other body tissues and environment? Are there any other animals usually do not recur once removed. Benign tumors may become malignant over time. affected? Are there any other signs of disease? Malignant tumors invade body tissues, spread to After completing a physical examination, your other body organs, recur if removed and often veterinarian may elect to perform some preliminary diagnostic procedures, such as lead to death. Melanomas usually grow very smears, scrapes, cultures or biopsies. Only a slowly taking up to 6 years to reach 1-1 Y i inches few of the many causes of lumps and bumps will in diameter. They are painless, but at later be discussed. stages may interfere with defecation, breeding and parturition. Some benign and malignant Flies tumors may eventually erode through the skin surface appearing as ulcerating lesions exuding The common , a mixture of melanin and blood. calcitrans, can be a source of lumps on your horse in the summer. Bites may appear over Melanomas may be successfully removed the back, belly, legs or ears and may be itchy surgically if local infiltrative growth is not to the horse. Since fly eggs are laid in rotting excessive, and if metastasis (spread to other organs) has not occurred. manure and hay, one method of control is proper manure disposal. Some horse owners Conclusions turn their animals out in the evening during the summer months to control stable fly bites. Fly Some cases of "lumps and bumps" may spray provides additional protection for your resolve, but all tumors should be examined by horse. your veterinarian as soon as possible. It is often impossible to determine the cause of a Dermatophilosis "lump" without a biopsy. In addition, without a precise biopsy diagnosis, the best method of This is a skin disease caused by a treatment will remain an unknown. In general, bacteria, Dermatophilus congolensis. The the larger the tumor and the longer it has been lesions consist of raised tufts of hair which are there, the harder it will be to treat. often referred to as "paint brush lesions" due to their resemblance to small paint brushes when removed from the horse. These raised areas often begin on the muzzle and spread over the Corine Farewell '89 is interested in equine back toward the tail. The lower legs are also medicine. commonly affected. The disease is commonly seen in horses that are kept outdoors in wet, rainy weather. Consequently, this condition is seen during the spring and summer months, and has attracted descriptive names such as "rain EQUINE GROUNDS

rot" and "rain scald." The animal will not be Equine Pastern Dermatitis ("scratches," "grease itchy but often feels pain when touched. The heel," "cracked heel") best therapy for this disease is to remove the animal from wet conditions. This is an acute, chronic dermatitis of the heel and pastern seen particularly in breeds with prominent "feathers" in the fetlock region. This condition has many potential causes. Nodular Collagenolytic Granuloma (Nodular Inadequate grooming and muddy, unsanitary, Necrobiosis) environments may predispose an animal to "scratches" in which the skin first becomes This is a common equine skin problem irritated or chapped. With continued exercise that is usually seen in spring and summer. The or irritation, the skin becomes inflamed and a nodules may be found on the neck, withers and foul-smelling discharge may be produced. In back. They are typically non-itchy and firm, addition, the condition can be due to and the overlying skin is normal. The cause of dermatophilosis, dermatophytosis (ringworm), this disease is unknown, however the nodules bacterial folliculitis, chorioptic mange, contact may regress spontaneously during the winter. If dermatitis (topical medicines and sprays, relief is desired during the summer for pasture plants), and photosensitization. cosmetic or work-related reasons, your Because there are so many possible causes for veterinarian should be consulted. The condition equine pastern dermatitis, and they all look the responds well to corticosteroids. same, it is very important to have diagnostic testing done early in the condition. Treatment may consist of clipping the hair and washing Allergic Reactions with a mild soap and water. It is important to keep the horse out of wet, muddy conditions Feed, environmental conditions, and drugs while healing takes place. Again, because there of any type have been reported to cause are so many possible causes, the most effective allergic-type responses in the horse. These treatment includes specific treatment directed eruptions do not have a characteristic against the cause as determined by laboratory appearance, but can resemble any kind of itchy tests. skin disease. Determining the precise cause of these allergic reactions can be a real challenge Skin diseases can be very frustrating for to the owner-veterinarian team. both the horseowner and the veterinarian and it is vital that a diagnosis be made in order to provide the proper treatment. With Bacterial Folliculitis (acne, heat rash) information provided by the owner, the veterinarian's task may be made easier. The cause of this disease is most commonly a bacteria, Staphlococcus aureus. Lesions occur in the saddle and harness areas and may be associated with poor grooming. Annemarie Bimbo is a senior student interested Again, spring and summer are the seasons when in large animal practice in New England you'll be most likely to see this disease, simply following graduation. because animals are used more at this time. The lesions appear as firm, often painful bumps which ooze, lose hair, and scab over. They are not itchy. With proper grooming care, the occurrence of this disease can be decreased. EQUINE B o u n d s

EQUINE ROUNDS

A Newsletter for Horsepeople

New York State College of Veterinary Medicine Cornell University, Ithaca, NY 14853

Guest Editor: Danny W. Scott, D.V.M. Student Editor : Luba Drouin

ADVISORY BOARD: Dr. John Lowe, Dr. Charles Rickard, Sue Stover '87, Luba Drouin '87, Marc A. Franz '88, Eden Bermingham 88', Corine Farewell '89, Matthew Belman '89, Karen Redmond. Permission to reprint any article must be obtained in writing.

Cornell University is an equal opportunity, affirmative action educator and employer.

OUR SPECIAL THANKS to DR. DANNY W. numerous case studies and review articles for SCOTT for his assistance in producing this issue textbooks and journals. His teaching has of Equine Rounds. Associate Professor Scott, centered on lecture-laboratory courses in an authority in the field of veterinary dermatology, immunology, endocrinology and dermatology, is a diplomate of the American clinical service teaching in the college's College of Veterinary Dermatology. He has teaching hospital. He received the Norden produced more than 180 publications, including Distinguished Teacher Award in 1976.

EQUINE ROUNDS Nonprofit Org. The New York State College of Veterinary Medicine U.S. Postage Cornell University PAID Ithaca, New York 14853 Cornell University

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